The invention relates to a low tire pressure alarm system for vehicles such as trucks and cars to prevent accidents due to tire rupture or dangerously reduced tire pressures.
The system monitors tire pressure, actually air mass, in each of basically four active tires of a vehicle on a continuing basis. Each wheel has a self-contained unit including an air-mass or pressure sensor cooperating with a power generator and a transmitter, all integrated into a single easily insertable and replaceable unit.
Information furnished by the wheel units is transmitted to a common receiver when the vehicle is moving, which displays an "O.K" indication when all signals are received as normal; or a warning condition, e.g., with a flashing light; and an alarm if there is a failure in any of the wheels.
In addition to the basic two-level alarm capability to detect incipient failure, the system is also capable of providing individual indication of the tires to identify which one of them might fail or has already lost pressure or gas mass.
The present system is completely fail-safe. Failure of any transmitter of the wheel units triggers the alarm system, except when the vehicle is at standstill, so that accidents can be prevented under all operating and weather conditions.
The entire wheel unit, including the sensor, power generator, and own antenna, is fastened to the inner periphery wall of the tire or alternatively to the outer rim of the steel wheel. It is important to note that there are no batteries in the wheel units, power being preferably obtained from the mechanical movement of a mechanism responsive to flexure of the tire as it flattens out on each revolution when going into contact with the road. Alternatively, this electro-magnetic power generator can be substituted by piezo-electric generating means, or by beamed power from the outside to each wheel from a single transmitter or from individual transmitters located near the wheels.
The invention also contemplates the use of a hand-held device, combining a transmitter and a receiver for ready indentification of the individual wheels or tires even on stationary vehicles, by walking up to the tire and getting a signal in response.
There is no wire between the centralized receiver and alarm unit, but antenna extensions may be brought to areas adjoining the wheels for increased safety of reception.
Tire inflation monitors have been known before, but they failed in one or more respects, so that the present invention is considered to constitute a major breakthrough and improvement over all hitherto known and used systems. There have been monitors that are locally applied to the wheels, there being no temperature evaluation devices for considering the temperature variations within the tire, thus reflecting inaccurate pressure differentials.